S&W 340Sc problem

[Alex4]

Hi,

Recently bought this revolver, seems not to fired much, however have noticed one problem: when opening cylinder it seems to be rubbing lower part of the barrel (in one picture you could see, it is shiny). When closed the cylinder gap seems eaven and even wider tha ideal (0.008). Also opening is not smooth (position when it is touching also in the photo). Do you know, what could be the issue and how to fox it? Since in Europe, sending to S&W is not an option unfortunately.

Best regards,
Alex

 

[michpatriot]

I had the same issue on a 340, I lightly stoned the sharp edges and polished the barrel. Others may say that's wrong but it worked for me. Carry it every day and haven't had any issue since.

 

[Alex4]

Thanks, michpatriot! Decided to follow your root and removed some metal using spyderco sharpmaker stones. Avoiding taking too much there is still some drag, but much less, than before, also applied some gun oil to the area.

 

[JDinAZ]

Looks like the forcing cone was not cut square. Which would give you more gap at top and less at bottom. Having the forcing cone trued up either by a gunsmith or doing it yourself would make a good bit of difference far as the angle issue goes

To address the rubbing on the bottom of the forcing cone when opening the cylinder. But not rubbing or dragging against the forcing cone when dry fire or live firing. That would most likely be a crane float issue. My 329pd crane would float in and out just a shade. It was caused by the new style crane screw having a spring loaded plastic tip in it. That tip will wiggle fore and aft which allows the crane to float fore and aft

When the crane floats forward when the cylinder is open this will let the cylinder shift forward ever so slightly and can allow the cylinder to rub the forcing cone.

A good tell tale sign of crane float is seeing a spot under the forcing cone on the frame where the crane smacks into the frame and creates a little gouge. My 329pd had that which is what made me get to wondering why it was doing that. Which lead me to finding out my crane floated fore and aft.

My 438 crane floats also. But not as much as the 329pd. To check crane float. Open cylinder and grab front of crane then pull it forward and push it aft. It should not move much if at all. If it does that's part of your issue.

Not much you can do about it other than maybe get a new crane screw and make a brass stub that replaces the plastic plunger and spring in there. Then fit it like and old school crane screw. The brass would wear over time but it won't cause the crane to wear and need replaced when it gets sloppy. Just do a new brass piece

Any catching type drag you feel when opening the cylinder at the point when you first give it force to open would be due to the cylinder bolt tip being a touch short. They don't hand fit the bolts anymore it's just an assembly from parts bin process. The new cylinder bolts all have the tip sitting below the face of the recoils shield. This makes you have to give them a nudge to open the cylinder.

Not much you can do about that unless you get an old steel j frame bolt and fit it to your new style manufacturing frame. You may have to build up the tip of the steel bolt then fit it so it's flush with the recoil shield. Also will most likely have to time the rear of it so the hammer passes properly for it to function in your gun.

There's also the burr on the center pin thing. The tip of the center pin is of course machined with a radiused tip. There is a sharp edge left where the machining was done. My 438 was sharp and made the same drag mark you see on your blast shield. Mine dug into the ramp when closing the cylinder. Same as what's showing on your gun. I very very lightly stoned the edge of that to smooth it then polished that edge very carefully. It no longer drags like it did and runs much smoother overall.

There's also endshake to take into consideration. When the cylinder is closed can you hold the cylinder by its sides and wiggle it fore and aft while locked into the frame. If so you have endshake which is way to fix with endshake shims

 

[slabside2]

Looks like the forcing cone was not cut square. Which would give you more gap at top and less at bottom. Having the forcing cone trued up either by a gunsmith or doing it yourself would make a good bit of difference far as the angle issue goes

To address the rubbing on the bottom of the forcing cone when opening the cylinder. But not rubbing or dragging against the forcing cone when dry fire or live firing. That would most likely be a crane float issue. My 329pd crane would float in and out just a shade. It was caused by the new style crane screw having a spring loaded plastic tip in it. That tip will wiggle fore and aft which allows the crane to float fore and aft

When the crane floats forward when the cylinder is open this will let the cylinder shift forward ever so slightly and can allow the cylinder to rub the forcing cone.

A good tell tale sign of crane float is seeing a spot under the forcing cone on the frame where the crane smacks into the frame and creates a little gouge. My 329pd had that which is what made me get to wondering why it was doing that. Which lead me to finding out my crane floated fore and aft.

My 438 crane floats also. But not as much as the 329pd. To check crane float. Open cylinder and grab front of crane then pull it forward and push it aft. It should not move much if at all. If it does that's part of your issue.

Not much you can do about it other than maybe get a new crane screw and make a brass stub that replaces the plastic plunger and spring in there. Then fit it like and old school crane screw. The brass would wear over time but it won't cause the crane to wear and need replaced when it gets sloppy. Just do a new brass piece

Any catching type drag you feel when opening the cylinder at the point when you first give it force to open would be due to the cylinder bolt tip being a touch short. They don't hand fit the bolts anymore it's just an assembly from parts bin process. The new cylinder bolts all have the tip sitting below the face of the recoils shield. This makes you have to give them a nudge to open the cylinder.

Not much you can do about that unless you get an old steel j frame bolt and fit it to your new style manufacturing frame. You may have to build up the tip of the steel bolt then fit it so it's flush with the recoil shield. Also will most likely have to time the rear of it so the hammer passes properly for it to function in your gun.

There's also the burr on the center pin thing. The tip of the center pin is of course machined with a radiused tip. There is a sharp edge left where the machining was done. My 438 was sharp and made the same drag mark you see on your blast shield. Mine dug into the ramp when closing the cylinder. Same as what's showing on your gun. I very very lightly stoned the edge of that to smooth it then polished that edge very carefully. It no longer drags like it did and runs much smoother overall.

There's also endshake to take into consideration. When the cylinder is closed can you hold the cylinder by its sides and wiggle it fore and aft while locked into the frame. If so you have endshake which is way to fix with endshake shims

This man knows his stuff.

 

[Alex4]

J.D., thanks for the valuable info! Now I also started to notice catch tipe drag could you please take a look at the foto and tell if "seeing a spot under the forcing cone on the frame where the crane smacks into the frame and creates a little gouge" is there, I understod it is there, though crane seems not to be floating. However I begin to suspect, crane indeed could be an issue, since cylinder is also touching frame (next picture), maybe revolver was dropped and crane bent ( it was second hand, yoke is a bit bent).One additional thing I notised is quite significant gap between crane and barrel sleeve on the right side, maybe the barrel is bent?

 

[Alex4]

And the pictures

 

[JDinAZ]

J.D., thanks for the valuable info! Now I also started to notice catch tipe drag could you please take a look at the foto and tell if "seeing a spot under the forcing cone on the frame where the crane smacks into the frame and creates a little gouge" is there, I understod it is there, though crane seems not to be floating. However I begin to suspect, crane indeed could be an issue, since cylinder is also touching frame (next picture), maybe revolver was dropped and crane bent ( it was second hand, yoke is a bit bent).One additional thing I notised is quite significant gap between crane and barrel sleeve on the right side, maybe the barrel is bent?

Glad to help anyway I can Alex

Yours looks pretty normal for a j frame. You can see a slight rub mark on the frame just below the forcing cone. But it doesn't look like from the pictures that it's gouged. If you drag your fingernail up towards the bottom of the forcing cone (as if gun was in vertical orientation) does your fingernail catch on a worn ridge there. Usually there's no powder burn mark on that spot as the metal rubs and "shears" off each time you close the cylinder so it's usually shiney

Since it doesn't look (from the last pics) that your crane is shearing into the frame. The catch type drag while closing the cylinder is most likely the small burr on the edge of the cylinder pin that drags on the recess prior to being pushed in by the blast shield as you close the cylinder. That's the very slight stone and polish I spoke about above.

Far as the cylinder gap goes. It's not out of the quiestion to have a non square face on the barrel at that location. But I honestly don't think, least from the pictures that your crane is bent. Usually if the crane is bent you have a hard time getting cylinder to lock into place in the frame when you close it. As in when closing the cylinder you have to really force the cylinder closed for the center pin to engage. Or you have to provide force in an odd direction to get the center pin to lock into place in the blast shield. As long as when you close it gently the center pin locks in easily I wouldn't worry about a bent crane.

Also check the end shake. Since yours doesn't look like the crane is gouging into the frame. If you have endshake (cylinder wiggles fore and aft when locked into frame. That would cause your cylinder face to drag on the way closed. They make shins for that. It forces the cylinder to the back, toward the blast shield, and takes up the slack. Start with 1 shim usually .002 and see. Add more as needed till cylinder doesn't float fore and aft anymore


I would deburr the center pin first. Then second check endshake and get that corrected if there is any. Then third check the BC gap with feeler gauge at top and bottom and right and left, four separate measurements to vector and variances, once you know for sure the cylinder has no endshake

 

[JDinAZ]

Alex. Also to add. None of those things makes what you have a bad gun. It's kinda expected after years of use that some maintenance can be needed. The only non normal wear and use / maintenance point is the smoothing of the edge of the center pin

 

[Alex4]

Dear J. D., ,thanks again! No, fingernail does not catches when drag down the frame from the forcing cone. Also, no unusual effort is required to close the cylinder, so hopefully indeed crane is not bent. Tried to polish a bit the edges of center pin as you advised (pressed spyderco triangle and spinning the cylinder), just slightly, not to overdo it, but action seems to be smoother now. There is some endshake indeed, but does not seem to too excessive. What I am afraid is that they could increase gap even further (or they wouldn't?), mine seems to be on a wider side. And of course to get them to Europe might be an issue, if someone considers them as firearm parts

 

[Alex4]

And pictures

 

[JDinAZ]

For the endshake, far as removing the endshake it's a good thing. The gap won't actually increase. The BC gap is the BC gap. But it will stay at a constant distance between cyl face and barrel/forcing cone entry point.

Smith factory BC gap tolerance has changed over the years. If I remember correctly, max is pretty huge nowadays, something like .010 to .012. But I do not have that documented number from smith. You could email their customer service and ask them, I'm sure they would tell you what that number is so you can check your gun.

(Which also brings up a thought, if you don't want to work on your own gun, ask them who is the factory service center for their product in your country. If they sell guns in your country they have to have some type of warranty service available to their customers there. Which would also mean there has to be a qualified gunsmith for the line in your country)

When you have endshake your gun is already firing at the widest gap possible, sometimes, and the narrowest gap possible, other times. Due to the cylinder floating fore and aft

Which while you are looking at the BC gap now, the widest gap you see may very well be with the cylinder at the back of the cylinder window already. Thus putting in endshake ships won't really change that. It will just take the float out of the cylinder, which as I mentioned could very well be why your cylinder rubs the barrel heel when closing the cylinder now

Use just enough to remove the endshake. Try to fit too many in there and you will bind the cylinder in the frame making it not turn freely. Start with one shim. Try it. Add one more. Try it. Etc. till it's as snug in frame window as you can get it without making the extractor star drag and bind against the blast shield. If it starts to drag or bind remove one shim and that's as far as you can go.


Far as legality there should be no restrictions, but what I would do is go to Brownells Europe site and contact them to see if they can ship endshake shims to you in your country

Brownells Europe - Firearms, Reloading Supplies, Gunsmithing Tools, Gun Parts and Accessories

Here's the brownells Europe part number for them

713100001
POWER CUSTOM PC-J2 .002 (.051mm) thick Smith & Wesson J Centerfire

 

[JDinAZ]

And pictures

From that pic, your gun doesn't appear to have a very high round count. There's not much wear on the ratchet (star shaped with reliefs that the hand contacts to advance cyl to next charging hole)